Fluid tubes are commonly used in HVAC systems, primarily in air handlers and similar cooling or heating systems. These systems are commonly used with cool or hot water, but could also be used to condense steam into a liquid in a beating system. Typically, these HVAC systems have a heat transfer medium, in the form of fluid. As used herein the term “fluid” covers both liquid, and steam. The fluid circulates throughout tubes to acquire or lose heat, usually from or to an air flow. The end of one rube is connected to the beginning of a next tube by a “return bend,” typically semicircular so that the next tube runs side-by-side with the one tube, crossing the air flow in the opposite direction. The common industry term for these HVAC heat transfer components is “coils.” The tubes in the coils are subject to damage when the fluid in the tubes is exposed to wide temperature differences, and as a result, is subject to changes in state. In the case of water, for instance, it will change from a liquid to a solid (ice) at low temperatures. At temperatures at or below 32° F. (0° C.), the water in the tubes is subject to freezing and the expansion of the water may result in splitting of the tubes.
Historically, ice masses form inside the tubes and expand outward creating excessive pressure in the tubes and at the return bends. The effect of freezing may cause the tubes to expand and split. Upon thawing, the water is released through the damaged tubes or return bends, thus flooding the air handler, an area around the air handler on the level the air handler resides, and any levels below. This may create a series of expensive repairs, not only to the coil and the frozen equipment but now to all building components that are around and below the area of the flooding. In addition, costly shut down time of offices, manufacturing spaces, labs and other building areas can result. This shut down time of operations of any facility requires emergency measures with possible excessive costs depending on the sensitivity of the operations involved.
Past tube or return bend damage prevention has taken the form of bladders, freeze plugs and various other devices. The use of these devices presents many problems to the maintainers of these systems. First and foremost, these devices, once they are activated, require labor to repair or replace. Furthermore, freeze plugs or rupture caps are designed to blow out in the event of excessive pressure caused by freezing, which results in flooding after the blow out of the plugs upon thawing of the ice.